There are three members of the mustelid family residing in
New Zealand, and none of them are welcome. Meet ferret, stoat and weasel.
Badgers, minks and otters are also mustelids. They seem a bit cuter, but then
they aren’t munching their way through our native bird populations.

All three species were bought to New Zealand from Europe in
the 1880’s to control our plaguing rabbit population. There is no doubt they
did prey on rabbits, as their numbers rapidly increased. Unfortunately, rabbits
weren’t the only meal on their menu. Our native species, having evolved with
only aerial predators, are naïve when it comes to these effective ground predators
that use smell to hunt.

Sadly between the three, they have decimated many of
our native bird, lizard and insect species.

So, who are they?

Ferret

The largest mustelid in New Zealand is the ferret.

Ferrets,
being somewhat hefty in stature, tend to remain on or close to the ground. They
are also more common in open country such as wetlands, riverbeds, dunes which
is unfortunately where our endangered bittern, black stilt, and various penguin
species reside.

They are also a threat to kiwi living in fragmented forest
patches and are big enough to kill an adult kiwi, which the other mustelid
members are not able to do.

Stoat

Stoats are next in size and have been touted as New Zealand’s
public enemy number one.

They are one of the three target species for Predator
Free 2050, along with rats and possums.

Stoats are implicated in the extinction
of our native bush wren, laughing owl, and native thrush and as the major cause
of decline of many others.

Along with rats, they caused the local extinction of
Marlborough’s mohua population on Mt Stokes in 2001.

Stoats
are the reason kiwi are declining at such a drastic rate. While adult kiwi are
big enough to fend for themselves, stoats can easily sniff out and target kiwi
chicks. As well as birds, stoats also enjoy a meal of lizards and insects.

Weasel

Weasels are the smallest of the mustelid family, and are
often confused as small stoats (check their tail: stoats have a black tip,
while weasels are a uniform brown).

Their size doesn’t reduce their ferocity,
but does reduce the size of the prey available to them. Having said that they
are still able to make a meal of eggs and chicks in the nest, as well as
lizards and invertebrates.

No one can deny mustelids are highly successful species and
their survival abilities deserve some respect. However, our native species have
existed for 55,000 years without mammalian predators. In the 150 to 250 years that most predators have been present in New
Zealand, they have not been able to evolve strategies to cope with mammalian
predators. They need our help and luckily advances in technology and science will
enable conservation managers to increase the tools in our toolbox through new
toxins, traps and lures.

Written by Wendy Sullivan, DOC, for the Marlborough Express. Images created by Nigel Hollyman, based on internet sources.